1. Field of the Invention
The present invention relates to a process for the preparation of alumina agglomerates of controlled porosity, which agglomerates possess exceptional mechanical strength, heat resistance and hydrothermal resistance.
2. Description of the Prior Art
A process for the regeneration of a composite catalyst containing alumina by heating the spent catalyst in a medium containing a major proportion of acetic acid and a minor proportion of hydrochloric acid is disclosed in U.S. Pat. No. 2,651,617. The heat treatment is at a temperature of from 200 to 250.degree. C. The process reduces the density of the spent catalyst by removing part of the alumina contained in the composite treated to thereby provide a porous particle. The acids are used in concentrated form, i.e., at least 60% strength by weight.
French Patent No. 1,222,830 discloses a process for the manufacture of alumina supports for catalysts which comprises treating the alumina at a temperature below 80.degree. C. in a concentrated acid medium to thereby dissolve a portion of it. The dissolved portion is then removed in the form of aluminum chloride by washing with water.
French Patent No. 1,386,364, of common assignee, discloses a process for preparing alumina agglomerates possessing a high mechanical strength. In the process disclosed, agglomerates of active alumina are treated in an autoclave in the presence of water, dried and then calcined at a temperature providing the specific surface area and desired pore size.
According to U.S. Pat. Nos. 3,628,914 and 3,480,389, also of common assignee, alumina agglomerates are prepared of even higher mechanical strength than that obtained according to French Patent No. 1,386,364 by treating agglomerates of active alumina with an acid in an autoclave.
It is an object of the present invention, however, to provide alumina agglomerates of exceptional mechanical strength, heat resistance and hydrothermal resistance.
It is another object of the present invention to provide a process which makes it possible to obtain alumina agglomerates possessing a controlled porosity together with exceptional mechanical strength, i.e., attrition resistance and crushing strength.
It is still another object of the present invention to provide a process for preparing alumina agglomerates possessing not only a controlled porosity and excellent mechanical strength at high temperatures, but even in the presence of steam so that the alumina agglomerates exhibit valuable heat stability and hydrothermal stability.
It is further an object of the present invention to provide a process for preparing alumina agglomerates possessing all of the aforementioned desirable characteristics, and which does not result in any loss of alumina, in contrast to those processes described in U.S. Pat. No. 2,651,617 and French Patent No. 1,222,830.
These and other objects, as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.